(i) Field of the Invention
This invention relates to a system to provide a means for maintaining electrical continuity between a point at the tow cable termination wrapped on the exterior of the large rotating drum to a fixed termination point external to the drum located on the winch base.
(ii) Description of the Prior Art
Towed sonar cables are highly complex, comprising a multiple core of individually insulated electrical conductors within a strain sheath capable of carrying the intense loads induced by the mass of the towed body plus the hydrodynamic drag of both body and streamed cable.
Whereas the strain sheath can terminate on the winch drum, it is necessary that the small electrical current carried by each of the conductors must terminate at the electronic signal processing centre within the ship. In many sonar systems presently in use, this is achieved by terminating each electrical cord at a slip ring element which is integral with the winch drum and from which a stationary brush picks off the signal current, transmitting the signal by a fixed electrical conductor to the electronic centre.
In view of the small currents and potentials involved, any deterioration in contact resistance between the slip ring and the brush can cause serious loss in sonar performance. Furthermore, since several dozen individual conductors are involved in a single cable, an equal number of individual slip rings and brushes are also required. In consequence, the slip ring mechanism becomes extremely complex, costly and subject to failure on any one or number of elements.
In an attempt to overcome slip ring problems, some oceanographic winches have the electrical pigtail or continuity cable extended through the cheek of the winch drum and wound on a secondary drum and arranged such that as the winch pays out the main cable, the pigtail spills into a pit below the winch and the free end of the pigtail plugs into the electronic system. This has the advantage of eliminating the slip rings. However, the process is somewhat random in which the cable gets tangled in the pit and can result in damage and breakdown.
Canadian Pat. No. 856,639 issued Nov. 24, 1974 to Alfred Kemeny, provided apparatus for storing such a flexible conductor e.g., electrical cables connected at one end to a fixed terminal point, and to a rotating drum disposed in spaced relation with respect thereto for the purpose of reeling in and paying out such cable of limited length in response to a sense of rotation of a reel. That patent also purported to provide the combination of reeling apparatus for paying out and reeling in a tow cable, and a cable storage device for the continuation of the cable intermediate a selected point and the winch drum.
That Kemeny patent proposed to provide apparatus to maintain continuity of a flexible conductor between a movable and static object wherein the conductor intermediate its end is wound onto a winch drum for paying out and reeling in the conductor. The patentee proposed to maintain electrical continuity between a variable depth sonar cable wound on a winch drum and the electronic signal processing equipment carried by the ship, and to circumvent the problems inherent in both slip ring mechanisms and the spilling of the pigtail into a storage pit.
The Kemeny patent purported to meet these objectives by providing a winch assembly including a cable anchored to a drum for reeling in and paying out cable in response to the sense of rotation of the drum and having a continuation of the cable extending from the drum and anchored to a selected location point. Apparatus was provided for storing the cable intermediate such location and the winch drum to prevent slack in the cable during reeling in and paying out of cable on the winch drum. The apparatus included a first storage drum connected to the winch drum for selected inter-related rotation movement of the respective drum. A second storage drum was disposed in selected space relation with the first drum. A winder member engaged to cable at positions in overlapping relation with respect to the respective storage drums and was movable about the periphery thereof for transferring the cable from one drum to the other during rotation of the winch drum.
In order to control slack in the cable, a helical spring was provided to impart a tortional bias force to the winder member. The spring was arranged that when the cable was being transferred in one direction between the rotating drum and the static drum, cable runs over the winder member and forces it to orbit against the spring bias forces of the helical spring. When cable was being transferred in the opposite direction, slack is fed off from the feed drum, to the winder member or forced to rotate in the opposite direction because of the spring forces applied against it so as to take up the slack.
Spring mechanisms of this sort discussed above have, however, proved to be unsatisfactory because they are subject to fatique and loss of spring temper. More importantly, however, it is difficult to maintain a substantially constant torque when there are a relatively large number of turns of the axis end of the torsion spring during a cable transferring operation. Thus, a finite limit is imposed on the cable transfer apparatus by the number of turns which can be accommodated by the spring.
Canadian Pat. No. 957,354 issued Nov. 5, 1979 to R. L. Fjarlie also related to such apparatus for transferring cable from a driven rotatable drum to an undriven static drum. It was directed especially to such apparatus which was adapted for use when the cable was an electric cable having signal voltages impressed thereon, and purported to provide an improvement in overcoming the deficiencies of such spring mechanism.
Fjarlie purported to overcome the problems discussed above by providing a cable transfer apparatus for transferring cable from a rotating drum to a static drum over a cable transfer sheave, wherein means were provided which were frictionally engaged by the one or the other of the rotatable or static drums, depending on which direction the rotatable drum is driven, and which served to maintain cable tension at all times. The transfer sheaves thereby accommodated cable transfer from a rotatable drum to a static drum, the limit of the number of turns to be transferred being determined by the finite storage capacity of the drums. The Fjarlie apparatus utilized frictional coupling means between the static and rotating drums on the one hand and the transfer sheave between them on the other hand, such that the frictional coupling action means together with cable tension served to maintain a driving torque against suitable arm means on which the transfer sheave was mounted.